everytime i try to delete big text message groupings my phone will lock up and most of the time will not delete them.....any tricks?

What messaging are you using? Handsent? Well with handsent I just delete it and you just have to not touch anything the phone for a while and it will delete. My advice would be to not let the messages get over a few hundred then delete.

I have the same problem is there any way to delete your SMS messages when your Evo is connected to your PC.?

Set your screen timeout to "never turn off", plug in your phone to the charging adapter and start deleting your SMS messages. After that, sit back and relax because it's going to take a pretty long time to delete all those When it's done, set the screen timeout back to how it was...

To set the screen timeout to "never turn off", you must go to Settings > Display > Screen timeout.